The invention pertains to aluminum-comprising layers extending over or within semiconductor wafer substrates, and pertains to methods of forming and polishing aluminum-comprising masses. Further, the invention pertains to methods of protecting aluminum within aluminum-comprising layers from electrochemical degradation during semiconductor processing.
Aluminum-comprising materials are frequently utilized in integrated circuitry formed on semiconductive wafers. The aluminum-comprising materials can consist essentially of elemental aluminum, or can comprise an alloy, such as aluminum/copper. Such aluminum-comprising materials are utilized as, for example, circuit components or conductive interconnects for electrically connecting circuit components.
A method of forming aluminum-comprising conductive interconnects is a damascene method. In a damascene method, a pattern of trenches is formed within an insulative material. An aluminum-comprising layer is then formed over the insulating material and within the trenches. The aluminum-comprising material is then planarized to remove portions of the material that are not within trenches.
The planarization typically comprises chemical-mechanical polishing utilizing a polishing pad to rub an abrasive slurry against the aluminum-comprising layer. Typically, the slurry comprises an aluminum oxide grit within an aqueous carrier solution. The slurry can have a pH of, for example, from about 2.5 to about 4.0. Example slurries are EP-A5655 (sold by Cabot), and XVS-6902 (sold by Rodel).
After desired abrasion of the aluminum-comprising layer, deionized water is flushed between the polishing pad and the layer to displace the polishing slurry from a surface of the aluminum-comprising layer. Typically, the polishing pad continues to spin relative to the surface as the water is provided between the pad and the surface. However, as the water does not comprise a grit, the abrasion of the aluminum-comprising layer is substantially reduced as the water displaces the slurry.
After the slurry is displaced, the polishing pad is separated from the aluminum-comprising layer, and the layer is rinsed with additional deionized water to further clean the polished surface. The rinsing can comprise spraying the layer with water, and/or submerging a wafer comprising the aluminum-comprising layer in a water bath. The water utilized for displacing the slurry, and for the rinse after displacing the slurry, typically has a pH of at least 7.0.
After the aluminum-comprising layer is rinsed with water, it is dried to remove the water before subsequent processing.
A difficulty which can occur during the above-described processing sequence is corrosion of a polished aluminum-comprising material. The corrosion can result in a loss of some or all of the aluminum-comprising material that is intended to remain on the wafer after the polishing process. If a relatively small amount of the material is lost, pits can occur within the aluminum-comprising material. If a larger amount of the material is lost, large crevices can be formed within the material.
Corrosion of an aluminum-comprising material can adversely affect physical properties of conductive lines formed from the aluminum-comprising material. For instance, conductance and strength of the aluminum-comprising material can be adversely affected. Also, pitting or crevice formation can decrease a surface planarity of a polished aluminum-comprising layer. As high surface planarity is frequently desirable for subsequent process steps, a decrease in surface planarity can adversely affect downstream fabrication processes utilizing the corroded aluminum-comprising layer. It would be desirable to develop alternative methods of processing aluminum-comprising layers wherein the above-described corrosion is avoided or at least reduced.
In one aspect, the invention encompasses a method of protecting aluminum within an aluminum-comprising layer from electrochemical degradation during semiconductor processing. A material that has a lower reduction potential than aluminum is provided within the layer.
In another aspect, the invention encompasses a semiconductor processing method of forming an aluminum-comprising line within an electrically insulative layer. An electrically insulative layer is formed over a semiconductive substrate. Trenches are formed within the electrically insulative layer. An aluminum-comprising layer is formed within the trenches and over the electrically insulative layer. The aluminum-comprising layer comprises a material that has a lower reduction potential than aluminum. The aluminum-comprising layer is planarized to form aluminum-comprising lines within the electrically insulative material.
In yet another aspect, the invention includes an aluminum-comprising layer over or within a semiconductor wafer substrate and comprising a material having a lower reduction potential than aluminum.